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Abstract:

According to one embodiment, there is provided a spin torque oscillator
including an oscillation layer formed of a magnetic material, a spin
injection layer formed of a magnetic material and configured to inject a
spin into the oscillation layer, and a current confinement layer
including an insulating portion formed of an oxide or a nitride and a
conductive portion formed of a nonmagnetic metal and penetrating the
insulating portion in a direction of stacking. The conductive portion of
the current confinement layer is positioned near a central portion of a
plane of a device region including the oscillation layer and the spin
injection layer.

Claims:

1. A spin torque oscillator comprising: an oscillation layer comprising a
magnetic material; a spin injection layer comprising a magnetic material
and configured to inject a spin into the oscillation layer; and a current
confinement layer comprising an insulating portion comprising an oxide or
a nitride and a conductive portion comprising a nonmagnetic metal and
penetrating the insulating portion in a direction of stacking, wherein
the conductive portion of the current confinement layer is positioned
near a central portion of a plane of a device region including the
oscillation layer and the spin injection layer.

2. The spin torque oscillator of claim 1, wherein the conductive portion
of the current confinement layer has a rectangular planar shape, the
device region including the oscillation layer and the spin injection
layer has a rectangular planar shape, and for at least three of four
sides of the rectangular conductive portion, the insulating portion is
arranged between each of the at least three sides of the conductive
portion and a corresponding one of four sides of the device region.

3. The spin torque oscillator of claim 1, wherein the current confinement
layer is 20% or more and 90% or less of the oscillation layer in width.

4. The spin torque oscillator of claim 1, wherein the current confinement
layer is positioned in a topmost surface.

5. A method of manufacturing the spin torque oscillator of claim 1,
comprising: forming a metal layer to be converted into a current
confinement layer on a stack including an oscillation layer comprising a
magnetic material and a spin injection layer comprising a magnetic
material; forming, on the metal layer, a mask layer with a tapered
surface at an end thereof; and oxidizing or nitriding an end of the metal
layer located under the mask layer formed to include the tapered surface
at the end thereof, to form a current confinement layer comprising an
insulating portion comprising an oxide or a nitride and a conductive
portion comprising a nonmagnetic metal and penetrating the insulating
portion in a direction of stacking.

6. A magnetic recording head comprising the spin torque oscillator of
claim 1, and a main pole.

7. A magnetic head assembly comprising: the magnetic recording head of
claim 6; a head slider with the magnetic recording head mounted thereon;
a suspension configured to hold the head slider at one end thereof; and
an actuator arm connected to another end of the suspension.

8. A magnetic recording apparatus comprising: a magnetic recording
medium; the magnetic head assembly of claim 7; and a signal processing
section configured to write and read a signal to and from the magnetic
recording medium using the magnetic recording head mounted in the
magnetic head assembly.

9. The magnetic recording apparatus of claim 8, wherein the spin torque
oscillator is provided on a trailing side of the main pole.

10. The magnetic recording apparatus of claim 8, wherein the spin torque
oscillator is provided on a leading side of the main pole.

Description:

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is based upon and claims the benefit of priority
from Japanese Patent Application No. 2010-270706, filed Dec. 3, 2010; the
entire contents of which are incorporated herein by reference.

FIELD

[0002] Embodiments described herein relate generally to a spin torque
oscillator, a method of manufacturing the same, a magnetic recording
head, a magnetic head assembly, and a magnetic recording apparatus.

BACKGROUND

[0003] The recording density of magnetic recording apparatuses is expected
to reach 1. Tbits/inch2 in the future as a result of development of
magnetic head techniques and perpendicular magnetic recording schemes.
However, even with the perpendicular magnetic recording scheme adopted,
achieving such a high recording density is not easy because of a thermal
fluctuation problem.

[0004] A high-frequency field assisted recording scheme has been proposed
in order to solve the thermal fluctuation problem. In the high-frequency
field assisted recording scheme, a magnetic recording medium is locally
subjected to an electric field of a high-frequency which is sufficiently
higher than a recording signal frequency and which is close to the
resonant frequency of the magnetic recording medium. As a result, the
magnetic recording medium with the high-frequency field applied thereto
resonates to reduce the coercivity (Hc) of the magnetic recording medium
to half of the original value. When the high-frequency field is thus
superimposed on the recording field, magnetic recording can be carried
out on a magnetic recording medium with a coercivity (Hc) and magnetic
anisotropic energy (Ku) which are higher than those in the conventional
one.

[0005] The use of a spin torque oscillator for generation of a
high-frequency electric field has been proposed. The spin torque
oscillator comprises two magnetic layers, a spin injection layer and an
oscillation layer. When a direct current is conducted through the spin
torque oscillator via an electrode, the spin injection layer generates
spin torque to subject magnetization in the oscillation layer to
ferromagnetic resonance. As a result, the spin torque oscillator
generates a high-frequency field. The spin torque oscillator is about
several tens of nanometers in size. Thus, the high-frequency electric
field generated is localized at a short distance of several tens of
nanometers from the spin torque oscillator. Moreover, an in-plane
component of the high-frequency electric field allows the perpendicularly
magnetized magnetic recording medium to resonate efficiently. This
enables a significant reduction in the coercivity of the magnetic
recording medium. As a result, magnetic recording is carried out only in
portions of the magnetic recording medium in which the recording field
provided by a main pole is superimposed on the high-frequency field
provided by the spin torque oscillator. This allows the use of a magnetic
recording medium that is high in coercivity (Hc) and magnetic anisotropic
energy (Ku). Hence, the thermal fluctuation problem, which may occur
during high density printing, can be avoided.

[0006] To provide a high-frequency field assisted recording head, it is
important to design and produce a spin torque oscillator which can
oscillate stably at a low current density and which can generate an
in-plane high-frequency field allowing the medium magnetization to
sufficiently resonate.

[0007] That is, when a current of an excessively high density is conducted
through the spin torque oscillator, heat generation and migration occur
to degrade the characteristics of the spin torque oscillator. Thus, the
maximum conductive current density is limited. Hence, it is important to
design a spin torque oscillator that can oscillate at as low a current
density as possible.

[0008] On the other hand, to allow the medium magnetization to
sufficiently resonate, the intensity of the in-plane high-frequency field
is desirably set to at least a certain level compared to the intensity of
an anisotropy field (Hk) in the medium. A possible method for increasing
the intensity of the in-plane high-frequency field is to increase one of
saturation magnetization in the oscillation layer, the thickness of the
oscillation layer, and the rotation angle of the magnetization in the
oscillation layer. However, all of these methods serve to increase the
current density.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009] A general architecture that implements the various features of the
embodiments will now be described with reference to the drawings. The
drawings and the associated descriptions are provided to illustrate the
embodiments and not to limit the scope of the invention.

[0010] FIG. 1 is a cross-sectional view of a spin torque oscillator
according to an embodiment;

[0011] FIGS. 2A, 2B, 2C and 2D are plan views showing examples of
arrangement of a conductive portion and an insulating portion of a
current confinement layer with respect to a device region;

[0012] FIG. 3 is a graph illustrating the relationship between a current
density required for oscillation and the number of sides of the
conductive portion for which the insulating portion is arranged between
each of these sides of the conductive portion and a corresponding one of
the four sides of the device region;

[0013] FIG. 4 is a diagram illustrating the relationship between the
current density required for oscillation and the ratio of the width of
the conductive portion of the current confinement layer to the width of
an oscillation layer;

[0014] FIGS. 5A, 5B, 5C, 5D, 5E and 5F are cross-sectional views
illustrating an example of a method of manufacturing a spin torque
oscillator according to the embodiment;

[0015] FIG. 6 is a diagram illustrating the dependence of the milling rate
of carbon on an ion milling angle;

[0016] FIG. 7 is a diagram illustrating the dependence, on the ion milling
angle, of the ratio of pattern width to mask width obtained after ion
milling;

[0017] FIG. 8 is a perspective view showing the internal structure of a
magnetic recording apparatus (HDD) according to an embodiment;

[0018] FIG. 9 is a perspective view showing a head stack assembly; and

[0019] FIG. 10 is an exploded perspective view showing the head stack
assembly.

DETAILED DESCRIPTION

[0020] Various embodiments will be described hereinafter with reference to
the accompanying drawings.

[0021] In general, according to one embodiment, there is provided a spin
torque oscillator including an oscillation layer formed of a magnetic
material, a spin injection layer formed of a magnetic material and
configured to inject a spin into the oscillation layer, and a current
confinement layer including an insulating portion formed of an oxide or a
nitride and a conductive portion formed of a nonmagnetic metal and
penetrating the insulating portion in a direction of stacking. The
conductive portion of the current confinement layer is positioned near a
central portion of a plane of a device region including the oscillation
layer and the spin injection layer.

[0022] FIG. 1 is a cross-sectional view of a spin torque oscillator
according to the embodiment. A spin torque oscillator 10 shown in FIG. 1
is structured so that an underlayer 11, a spin injection layer 12, an
intermediate layer 13, an oscillation layer 14, and a current confinement
layer 15 are stacked in this order. The current confinement layer 15
includes an insulating layer 16 comprising an oxide or a nitride and a
conductive portion 17 comprising a nonmagnetic metal and penetrating the
insulating portion 16 in the direction of stacking.

[0023] The underlayer 11 functions to control the crystal orientation of
the spin injection layer 12 but need not necessarily be provided. On the
other hand, a protect layer may be provided between the oscillation layer
14 and the current confinement layer 15 as required in order to protect
the oscillation layer 14 from damage caused by oxidation.

[0024] The spin torque oscillator 10 may include a pair of electrodes
configured to allow a drive current to conduct through the direction of
stacking of the stacked film. However, the electrodes may be a main
electrode or shield (or return pole) of a magnetic head. In this case, at
least one of the electrodes of the spin torque oscillator may be omitted.
Furthermore, the spin torque oscillator may be provided on a trailing
side or a leading side of the main pole. In the following description,
the spin torque oscillator includes a pair of electrodes. An external
field Hex is applied to the spin torque oscillator. A gap field generated
between the electrodes causes an external field perpendicular to a film
surface to be applied to the spin torque oscillator. The magnetization in
the oscillation layer causes precession around an axis which is almost
perpendicular to the film surface and which serves as the axis of
rotation. Thus, high-frequency field is externally generated.

[0025] An FeCoAl alloy having in-plane magnetic anisotropy can be used as
the oscillation layer. Alternatively, the oscillation layer may be formed
of a material comprising an FeCoAl alloy to which at least one element
selected from a group consisting of Si, Ge, Mn, Cr, and B is added. This
allows adjustment of, for example, the saturation magnetic flux density
(Bs), anisotropy field (Hk), and spin torque transmissivity of the
oscillation layer and the spin injection layer.

[0026] A material with a high spin transmittance, for example, Cu, Au, or
Ag may be used as the intermediate layer. The thickness of the
intermediate layer desirably ranges from the thickness of one atom layer
to 3 nm. The use of such an intermediate layer allows exchange coupling
between the oscillation layer and the spin injection layer to be adjusted
to an optimum value.

[0027] The spin injection layer may be appropriately formed of a material
excellent in perpendicular orientation, for example, a CoCr-based
magnetic layer such as CoCrPt, CoCrTa, CoCrTaPt, or CoCrTaNb in which
magnetization is oriented perpendicularly to the film surface, an
RE-TM-based amorphous alloy magnetic layer such as TbFeCo, a Co
artificial-lattice magnetic layer such as Co/Pd, Co/Pt, or CoCrTa/Pd, a
CoPt- or FePt-based alloy magnetic layer, or an SmCo-based alloy magnetic
layer; a soft magnetic layer such as CoFe, CoNiFe, NiFe, CoZrNb, FeN,
FeSi, or FeAlSi which has a relatively high saturation magnetic density
and which is magnetically anisotropic in an in-plane direction; a Heusler
alloy selected from a group consisting of CoFeSi, CoMnSi, and CoMnAl; or
a CoCr-based magnetic alloy film in which magnetization is oriented in
the in-plane direction. A plurality of materials selected from the
above-described groups may be used in a stack for the spin injection
layer.

[0028] A nonmagnetic metal material that is low in electric resistance,
such as Ti, Cu, Ru, or Ta, may be used as the underlayer and the protect
layer.

[0029] The current confinement layer includes the conductive portion
comprising a nonmagnetic material such as Ti, Cu, Ru, or Ta which is low
in electric resistance and the insulating portion comprising an oxide
such as SiO2 or Al2O3, a nitride such as SiN, or an oxide
or a nitride of the nonmagnetic metal forming the conductive portion. A
current path can be controlled by controlling the arrangement of the
conductive portion and insulating portion of the current confinement
layer.

[0030] FIGS. 2A to 2D show examples of arrangement of the conductive
portion and insulating portion of the current confinement layer with
respect to a device region including the oscillation layer and the spin
injection layer. The device region including the oscillation layer and
the spin injection layer has a rectangular planar shape. The conductive
portion of the current confinement layer has a rectangular planar shape.
The arrangements shown in FIGS. 2A to 2D are different from one another
in the number of those of the four sides of the rectangular conductive
portion for which the insulating portion is arranged between each of
these sides of the conductive portion and a corresponding one of the four
sides of the device region.

[0031] In FIG. 2A, for none of the four sides of the rectangular
conductive portion, the insulating portion is arranged between each of
these sides of the conductive portion and a corresponding one of the four
sides of the device region; FIG. 2A shows a conventional example. In FIG.
2B, for two of the four sides of the rectangular conductive portion, the
insulating portion is arranged between each of these sides of the
conductive portion and a corresponding one of the four sides of the
device region is two; FIG. 2B shows a comparative example. In FIG. 2C,
for three of the four sides of the rectangular conductive portion, the
insulating portion is arranged between each of these sides of the
conductive portion and a corresponding one of the four side of the device
region is three; FIG. 2C shows an embodiment. In FIG. 2D, for all of the
four sides of the rectangular conductive portion, the insulating portion
is arranged between each of these sides of the conductive portion and a
corresponding one of the four sides of the device region is four; FIG. 2D
shows another embodiment.

[0032] FIG. 3 is a graph illustrating the relationship between a current
density required for oscillation and the number of those of the four
sides of the rectangular conductive portion for which the insulating
portion is arranged between each of these sides of the conductive portion
and a corresponding one of the four sides of the device region (the
numbers in FIG. 3 correspond to FIGS. 2A to 2D). FIG. 3 shows the results
of determination, through simulation, of a drive current required for
oscillation with the size of the device region set to 50 nm×50 nm
and with the arrangement of the conductive portion of the current
confinement layer with respect to the device region varied.

[0033] FIG. 3 indicates that the drive current can be reduced by
increasing the number of those of the four sides of the rectangular
conductive portion for which the insulating portion is arranged between
each of these sides of the conductive portion and a corresponding one of
the four sides of the device region, that is, the drive current can be
reduced by arranging the conductive portion, corresponding to a drive
current path, closer to a central portion of the device region.

[0034] When the spin torque oscillator is oscillated at a high frequency,
saturation of an oscillation state starts from the central portion of the
oscillation layer. Thus, even with a low drive current, the oscillation
state of the central portion of the oscillation layer can be promoted by
arranging the drive current path in the central portion of the
oscillation layer.

[0035] FIG. 4 is a diagram illustrating the relationship between the
current density required for oscillation and the ratio of the width of
the conductive portion of the current confinement layer to the width of
the oscillation layer which relationship is observed when the conductive
portion of the current confinement layer is located in the central
portion of the device region (which is 50 nm×50 nm in size), i.e.,
the case corresponding to FIG. 2D. FIG. 4 indicates that the width of the
conductive portion of the current confinement layer is preferably 20% or
more and 90% or less of the width of the oscillation layer. When the
width of the conductive portion is larger than 90% of the width of the
oscillation layer, the effect of reducing the oscillation current density
is hard to be exerted. When the width of the conductive portion is
smaller than 20% of the width of the oscillation layer, oscillation
occurs in the spin injection layer and is thus unlikely to occur in the
oscillation layer. Thus, the effect of reducing the oscillation current
density is hard to be exerted.

[0036] The current confinement layer may be arranged as a nonmagnetic
layer other than the spin injection layer and oscillation layer, which
are magnetic layers, and may be arranged as one of the topmost surface
layer (cap layer), intermediate layer, and underlayer of the spin torque
oscillator or as a plurality of these layers. However, the current
confinement layer is preferably arranged as the topmost surface layer of
the spin torque oscillator. For the spin torque oscillator with the
current confinement layer provided as the topmost surface layer, the
impact, on the crystal structure, of the spin injection layer and
oscillation layer, which are magnetic layers, is negligible. Furthermore,
when a protect layer is provided between the oscillation layer and the
current confinement layer, oxygen or nitrogen present in the insulating
portion of the current confinement layer can be restrained from diffusing
to the oscillation layer.

[0037] [Method of Manufacturing a Spin Torque Oscillator]

[0038] FIGS. 5A to 5F are cross-sectional views illustrating an example of
a method of manufacturing a spin torque oscillator according to the
embodiment.

[0039] As shown in FIG. 5A, for example, the following layers are
deposited on the main pole 20: an underlayer 11, a spin injection layer
12, an intermediate layer 13, an oscillation layer 14, a metal layer 21
to be converted into a current confinement layer, and a hard mask layer
22. A resist is applied to the hard mask layer 22, and then a resist
pattern 23 of a predetermined geometry is formed. The resist pattern 23
can be formed using a stepper. However, the resist pattern 23 may be
formed by writing with an electron beam or nanoimprinting.

[0040] As shown in FIG. 5B, the resist pattern 23 is transferred to the
hard mask layer 22 using reactive ion etching (RIE).

[0041] The resist pattern 23 may be used as an ion milling mask without
any change. However, when the pattern size is reduced to increase the
aspect ratio of the resist pattern 23, collapse of the pattern may occur.
To avoid this, the resist pattern 23 needs to be reduced in height.
However, the reduced height of the resist pattern 23 makes processing of
the spin torque oscillator by ion milling difficult. Thus, the
resistance, to ion milling, of the hard mask layer 22 to which the
pattern is transferred needs to be increased with decreasing device size
of the spin torque oscillator.

[0042] Examples of the hard mask layer 22 include carbon (C), Si, Ta, Ti,
and Al2O3. However, the hard mask layer 22 is not particularly
limited provided that the hard mask layer 22 resists ion milling. If for
example, carbon is used as the hard mask layer 22, the hard mask layer 22
is etched by oxygen RIE. Furthermore, a second hard mask layer comprising
Si, for example, may be provided between the resist and the hard mask
layer 22 formed of carbon. The second hard mask layer formed of Si etc.
can be etched using halogen gas and appropriately resists etching based
on oxygen RIE. Thus, the second hard mask layer serves to improve etching
selectivity to resist and carbon.

[0043] As shown in FIG. 5C, the metal layer 21, the oscillation layer 14,
the intermediate layer 13, the spin injection layer 12, and the
underlayer 11 are removed from regions exposed from the pattern of the
hard mask layer 22 by ion milling. Moreover, the film thickness of the
main pole 20 is partly reduced. At this time, redeposition and a taper
angle can be controlled by controlling the height of the hard mask layer
22 and an ion milling angle. The ion milling angle is between the film
surface of the hard mask layer 22 and an ion irradiation direction. As
described below, the pattern of the hard mask layer 22 can be shaped like
a barrel roof or a trapezoid with tapered surfaces at ends thereof.

[0044] FIG. 6 illustrates the dependence of the milling rate of carbon on
the ion milling angle. As shown in FIG. 6, the milling rate of carbon is
greatest at an ion milling rate of about 50 degrees.

[0045] When milling is carried out with the ion milling angle set to 0
degree, that is, with ions emitted perpendicularly to the film surface,
corners of the pattern of the hard mask layer 22 are removed. Thus,
tapered surfaces inclined at about 50 degrees to the upper film surface
are formed at the respective ends of the hard mask layer 22. When the
milling is continued with the ion milling angle kept at 0 degree, the
tapered surfaces at the respective ends of the hard mask layer 22 are
milled at an ion milling angle of about 50 degrees. At this time, the
milling rate of carbon is high at the tapered surfaces, allowing the
pattern of the hard mask layer 22 to be shaped like a barrel roof or a
trapezoid with the tapered surfaces at the ends thereof.

[0046] FIG. 7 illustrates the dependence, on the ion milling angle, the
ratio of the pattern width to the mask width obtained after the ion
milling. Setting the ion milling angle to smaller than 50 degrees causes
redeposition, increasing the ratio of the pattern width to the mask
width. Setting the ion milling angle to greater than 50 degrees, for
example, 80 degrees, causes side etching, reducing the ratio of the
pattern width to the mask width.

[0047] Thus, first, the ion milling angle is set to about 50 degrees. The
metal layer 21, the oscillation layer 14, the intermediate layer 13, the
spin injection layer 12, the underlayer 11, and a part of the main pole
20 are removed at a high milling rate. A mask shape is then transferred.
Thereafter, the ion milling angle is set to 0 degrees. The pattern of the
hard mask layer 22 is shaped to include tapered surfaces at the ends
thereof. Then, the ion milling angle is set to about 80 degrees to
prevent redeposition. Hence, the pattern of the hard mask layer 22 can be
formed to have the desired shape.

[0048] As shown in FIG. 5D, a buried insulating layer 24 is deposited on
the sides of the underlayer 11, spin injection layer 12, intermediate
layer 13, and oscillation layer 14 on the main pole 20. Examples of a
material for the buried insulating layer 24 generally include SiO2
and Al2O3. However, the material is not particularly limited.
Moreover, the buried insulating layer 24 is etched back by RIE or ion
milling so as to expose the pattern of the hard mask layer 22. Burying
the insulating layer allows the side walls of the layers other than the
metal layer 21, formed in the topmost surface of the spin torque
oscillator, to be restrained from being oxidized (nitrided).

[0049] As shown in FIG. 5E, the hard mask layer is removed by RIE using
oxygen gas to convert the metal layer 21 into a current confinement layer
15 with an insulating layer 16 and a conductive portion 17 formed of a
nonmagnetic metal and penetrating the insulating portion 16 in the
direction of stacking. That is, the insulating portion 16 can be formed
for the following reason. In the pattern of the hard mask layer 22, the
tapered portions located at the ends of the hard mask /layer 22 is
removed first because of the small thickness thereof, and only the ends
of the metal layer 21, located under the tapered portions of the hard
mask layer 22, is oxidized. Incidentally, before the removal of the
pattern of the hard mask layer 22, the ion implantation may be used to
implant oxygen ions or nitride ions into the ends of the metal layer 21
to produce the insulating portion 16.

[0050] In the ion milling method, etching is carried out with an
acceleration voltage set to about several hundred volts. However, in the
ion implantation method, ions can be implanted with the acceleration
voltage set to several kilovolts to several tens of kilovolts without
etching. Here, since the pattern of the hard mask layer 22 is shaped like
a barrel roof, oxygen ions or nitrogen ions can be implanted deeper
through the ends of the pattern of the hard mask layer 22, which are
small in film thickness.

[0051] Furthermore, either method may result in formation of a thin
insulating film (oxide film or nitride film) on the surface of the
conductive portion. Thus, after the removal of the hard mask layer, ion
milling or bias sputter etching may be carried out to remove the current
confinement layer 15 by about 3 to 10 nm. Such treatment allows removal
of the insulating film formed in the conductive portion 17 of the current
confinement layer 15. At this time, the range of the insulating portion
can be adjusted by, for example, regulating an ion milling rate.

[0052] As shown in FIG. 5F, a shield 25 formed of NiFe, for example, is
deposited on the current confinement layer 15 and the buried insulating
layer 24. As described above, the spin torque oscillator 10 with the
current confinement layer 15 in the topmost surface can be manufactured.

EXAMPLES

Example 1

[0053] A spin torque oscillator was manufactured using the method
illustrated in FIGS. 5A to 5F.

[0054] Ru, CoCrPt, Cu, FeCoAl, Ti, Si, and carbon (C) were deposited on
the main pole 20. Ru was deposited to a thickness of 15 nm and served as
an underlayer 11. CoCrPt was deposited to a thickness of 20 nm and served
as a spin injection layer 12. Cu was deposited to a thickness of 3 nm and
served as an intermediate layer 13. FeCoAl was deposited to a thickness
of 13 nm and served as an oscillation layer 14. Ti was deposited to a
thickness of 20 nm and served as a metal layer 21 to be converted into
the current confinement layer. Si was deposited to a thickness of 5 nm
and served as a hard mask layer 22. Carbon (C) was deposited to a
thickness of 70 nm. Then, a resist was applied to the hard mask layer 22,
and thereafter a resist pattern 23 of a predetermined geometry was
formed. Ion milling was carried out so as to set the device size to 50
nm×50 nm. The metal layer 21 formed of Ti was converted into a
current confinement layer 15 by RIE using oxygen gas. The current
confinement layer 15 was etched by 3 nm by means of bias sputtering.
Thereafter, a shield 25 was deposited on the current confinement layer
15. Thus, a spin torque oscillator was manufactured.

[0055] The width of the insulating portion 16 was measured by energy
dispersive X-ray diffraction (EDX). The results of the measurement
indicate that the insulating portion 16 was present down to a depth of
about 3 nm (oxygen advanced to a depth of 6 nm including the portion
removed by etching) and that the depth corresponded to 50% of the width
of the oscillation layer 14.

[0056] When the spin torque oscillator was driven, oscillation at 25 GHz
was observed in the oscillation layer 14. The high-frequency power was
2.0×10-18 V2/Hz, and the oscillation current density was
8.1×107 A/cm2.

Example 2

[0057] As is the case with Example 1, an underlayer 11, a spin injection
layer 12, an intermediate layer 13, an oscillation layer 14, a metal
layer 21, and a hard mask layer 22 were deposited on the main pole 20. A
resist pattern 23 was then was formed. Ion milling was carried out so as
to set the device size to 50 nm×50 nm. The metal layer 21 formed of
Ti was converted into a current confinement layer 15 by implanting oxygen
ions through the pattern of the hard mask layer 22. The current
confinement layer 15 was etched by 6 nm by means of bias sputtering.
Thereafter, a shield 25 was deposited on the current confinement layer
15. Thus, a spin torque oscillator was manufactured. According to Example
1, by etching the current confinement layer 15 by about 6 nm, an oxide
film formed during removal of the hard mask layer would be all removed.
Hence, the remaining insulating portion 16 was formed by implantation of
oxygen ions.

[0058] The width of the insulating portion 16 was measured by EDX. The
results of the measurement indicate that the insulating portion 16 was
present down to a depth of about 7 nm and that the depth corresponded to
50% of the width of the oscillation layer 14.

[0059] When this spin torque oscillator was driven, oscillation at 25 GHz
was observed in the oscillation layer 14. The high-frequency power was
2.0×10-18 V2/Hz, and the oscillation current density was
7.8×107 A/cm2.

Example 3

[0060] As is the case with Example 1, an underlayer 11, a spin injection
layer 12, an intermediate layer 13, an oscillation layer 14, a metal
layer 21, and a hard mask layer 22 were deposited on the main pole 20. A
resist pattern 23 was then formed. Ion milling was carried out so as to
set the device size to 50 nm×50 nm. The metal layer 21 formed of Ti
was converted into a current confinement layer 15 by implanting oxygen
ions through the pattern of the hard mask layer 22. The current
confinement layer 15 was etched by 6 nm by means of bias sputtering.
Thereafter, a shield 25 was deposited on the current confinement layer
15. Thus, a spin torque oscillator was manufactured. According to Example
1, by etching the current confinement layer 15 by about 6 nm, the oxide
film formed during removal of the hard mask layer would be all removed.
Hence, the remaining insulating portion 16 was formed by implantation of
oxygen ions.

[0061] The width of the insulating portion 16 was measured by EDX. The
results of the measurement indicate that the insulating portion 16 was
present down to a depth of about 7 nm and that the depth corresponded to
50% of the width of the oscillation layer 14.

[0062] When the spin torque oscillator was driven, oscillation at 25 GHz
was observed in the oscillation layer 14. The high-frequency power was
2.0×10-18 V2/Hz, and the oscillation current density was
8.3×107 A/cm2.

Comparative Example 1

[0063] A spin torque oscillator was manufactured in the same manner as
that in Example 1 except that the current confinement layer 15 was etched
by 6 nm by means of bias sputtering before the shield was deposited.
According to Example 1, by etching the current confinement layer 15 by 6
nm, the oxide film formed during removal of the hard mask layer was all
removed.

[0064] EDX was used to determine that no current confinement layer was
present into which the metal layer formed of Ti was converted but that
only the Ti conductive portion was present.

[0065] When the spin torque oscillator was driven, oscillation at 25 GHz
was observed in the oscillation layer 14. The high-frequency power was
2.0×10-18 V2/Hz. This indicates that the high-frequency
power in Comparative Example 1 was not lower than that in the examples.
Furthermore, the oscillation current density was 1.7×108
A/cm2. This indicates that the spin torque oscillators in Examples 1
to 3 each of which included the current confinement layer were lower than
that in Comparative Example 1 in oscillation current density.

[0066] Table 1 shows the oscillation current density and high-frequency
power in Examples 1 to 3 and Comparative Example 1.

[0067] Now, a magnetic head assembly and a magnetic recording apparatus
(HDD) both using the above-described spin torque oscillator will be
described.

[0068] FIG. 8 is a perspective view showing the internal structure of a
magnetic recording apparatus (HDD) according to the embodiment. As shown
in FIG. 8, HDD comprising a housing 110. The housing 110 includes a base
112 shaped like a rectangular box with an open top surface, and a top
cover 114 locked to the base with screws 111 to close the opening at the
upper end of the base. The base 112 includes a rectangular bottom wall
112a and a side wall 112b provided upright along the periphery of the
bottom wall.

[0069] One magnetic disk 116 and a spindle motor 118 are provided inside
the housing 110; the magnetic disk 116 serves as a recording medium, and
the spindle motor 118 serves as a driving section configured to support
and rotate the magnetic disk. The spindle motor 118 is disposed on the
bottom wall 112a. The housing 110 is formed to have a size enough to
accommodate a plurality of magnetic disks, for example, two magnetic
disks. The spindle motor 118 is formed to be able to support and drive
two magnetic disks.

[0070] A plurality of magnetic heads 117, a head stack assembly
(hereinafter referred to as HSA) 122, a voice coil motor (hereinafter
referred to as VCM) 124, a lamp load mechanism 125, a latch mechanism
126, and a substrate unit 121 are housed in the housing 110. The magnetic
heads 117 record and reproduce information on and from the magnetic disk
116. HAS 122 movably supports the magnetic heads over the magnetic disk
116. VCM 124 pivotally moves and positions HSA. The lamp load mechanism
125 holds HSA in a retracted position where the magnetic disk is separate
from the magnetic disk when the magnetic head has moved to the outermost
periphery of the magnetic disk. The latch mechanism 126 holds HSA in a
retracted position when an impact or the like acts on HDD. The substrate
unit 121 includes a preamplifier. A print circuit board (not shown in the
drawings) is screwed to an outer surface of a bottom wall 112a of the
base 112. The print circuit board controls the operation of the spindle
motor 118, VCM 124, and the magnetic heads via the substrate unit 121. A
circulation filter 123 is provided in the side wall of the base 112 to
catch dust generated inside the housing as a result of operation of the
movable section. The circulation filter 123 is positioned outside the
magnetic disk 116.

[0071] The magnetic disk 116 is formed, for example, to have a diameter of
65 mm (2.5 inches) and includes a magnetic recording layer in both the
top and bottom surfaces thereof. The magnetic disk 116 is coaxially
fitted around a hub (not shown in the drawings) of the spindle motor 118,
and is fixedly clamped to the hub by a clamp spring 127. Thus, the
magnetic disk 116 is supported parallel to the bottom wall 112a of the
base 112. The magnetic disk 116 is rotated at a predetermined speed, for
example, at 5,400 rpm or 7,200 rpm, by the spindle motor 118.

[0072] FIG. 9 is a perspective view showing the head stack assembly (HSA)
122 according to the embodiment. FIG. 10 is an exploded perspective view.
As shown in FIG. 9 and FIG. 10, HSA 122 comprises a bearing portion 128,
two head gimbal assembly (hereinafter referred to as HGA) 130 extending
from the bearing portion, a spacer ring 144 arranged between HGAs in a
stacked manner, and a dummy spacer 150.

[0073] The bearing portion 128 is positioned away from the center of
rotation of the magnetic disk 116 along a longitudinal direction of the
base 112. The bearing portion 128 includes a pivot shaft 132 provided
upright on the bottom wall 112a of the base 112 and a cylindrical sleeve
136 supported coaxially with the pivotal shaft 132 so as to be rotatable
via a bearing 134. The sleeve 136 includes an annular flange 137 formed
at an upper end of the sleeve 136 and a threaded portion 138 formed on
the outer periphery of a lower end thereof. The sleeve 136 of the bearing
portion 128 is formed to have a size, in this case, a mountable axial
length enough to allow a maximum number of HGAs, for example, four HGAs
and spacers each positioned between two adjacent HGAs to be mounted on
the sleeve 136 in a stacked manner.

[0074] In the embodiment, since the number of magnetic disks 116 is set to
one, two HGAs 130, the number of which is smaller than the mountable
maximum number of four, are provided on the bearing portion 128. Each HGA
includes an arm 140 extending from the bearing portion 128, a suspension
142 extending from the arm, and the magnetic head 117 supported at an
extension end of the suspension via a gimbal portion.

[0075] The arm 140 is formed like a thin flat plate by stacking stainless
steel, aluminum, and stainless steel. The arm 140 includes a circular
through-hole 141 formed at one end, that is, a base end thereof. The
suspension 142 is formed by an elongate leaf spring with a base end
thereof fixed to a leading end of the arm 140 by spot welding or bonding.
The suspension 142 extends from the arm. The suspension 142 and the arm
140 may be integrally formed of the same material.

[0076] The magnetic head 117 includes a substantially rectangular slider
(not shown in the drawings), and a recording head and a reproducing
CPP-GMR head according to the embodiment both formed on the slider. The
magnetic head 117 is fixed to the gimbal portion formed at the leading
end of the suspension 142. Furthermore, the magnetic head 117 includes
four electrodes (not shown in the drawings). A relay flexible print
circuit board (hereinafter referred to as the relay FPC; not shown in the
drawings) is installed on the arm 140 and the suspension 142. The
magnetic head 117 is electrically connected to a main FPC 121b via the
relay FPC.

[0077] The spacer ring 144 is formed of aluminum or the like so as to have
a predetermined thickness and a predetermined outer diameter. A support
frame 146 comprising a synthetic resin is integrally formed on the spacer
ring 144. The support frame 146 extends outward from the spacer ring. A
voice coil 147 of VCM 124 is fixed to the support frame 146.

[0078] The dummy spacer 150 includes an annular spacer main body 152 and a
balance adjustment section 154 extending from the spacer main body. The
dummy spacer 150 is formed, for example, integrally with metal such as
stainless steel. The spacer main body 152 is formed to have an outer
diameter equal to that of the spacer ring 144. That is, a portion of the
spacer main body 152 which is contacted by the arm is formed to have an
outer diameter equal to that of a portion of the spacer ring 144 which is
contacted by the arm. Furthermore, the spacer main body 152 is formed to
have a thickness equal to the sum of the thickness of the arms of less
than the maximum number of HGAs, in this case, two HGAs, that is, the
thickness corresponding to the two arms, and the thickness of the spacer
ring arranged between the arms.

[0079] The dummy spacer 150, the two HGAs 130, and the spacer ring 144 are
fitted around the outer periphery of the sleeve 136 of the bearing
portion 128 so that the sleeve 136 of the bearing portion 128 is inserted
through an inner hole in the spacer main body 152, the through-hole 141
in the arm 140, and an inner hole in the spacer ring. The dummy spacer
150, the two HGAs 130, and the spacer ring 144 are arranged on the flange
137 along the axial direction of the sleeve in a stacked manner. The
spacer main body 152 of the dummy spacer 150 is fitted around the outer
periphery of the sleeve 136 so as to be sandwiched between the flange 137
and one of the arms 140. The spacer ring 144 is fitted around the outer
periphery of the sleeve 136 so as to be sandwiched between the two arms
140. Moreover, an annular washer 156 is fitted around the outer periphery
of the lower end sleeve 136.

[0080] The dummy spacer 150, two arms 140, spacer ring 144, and washer 156
all fitted around the outer periphery of the sleeve 136 are sandwiched
between the flange 137 and a nut 158 screwed to the threaded portion 138
of the sleeve 136. The dummy spacer 150, two arms 140, spacer ring 144,
and washer 156 are thus fixedly held on the outer periphery of the sleeve
136.

[0081] The two arms 140 are placed at predetermined positions with respect
to a circumferential direction of the sleeve 136. The two arms 140 extend
in the same direction from the sleeve. Thus, the two HGAs can move
pivotally integrally with the sleeve 136 and are located opposite each
other at a predetermined distance from the respective surfaces of the
magnetic disk 116. Furthermore, the support frame 146 integrated with the
spacer ring 144 extends from the bearing portion 128 in a direction
opposite to that in which the arms 140 extend. Two pin-shaped terminals
160 projects from the support frame 146. The terminals are electrically
connected to the voice coil 147 via wiring (not shown in the drawings)
embedded in the support frame 146.

[0082] While certain embodiments have been described, these embodiments
have been presented by way of example only, and are not intended to limit
the scope of the inventions. Indeed, the novel embodiments described
herein may be embodied in a variety of other forms; furthermore, various
omissions, substitutions and changes in the form of the embodiments
described herein may be made without departing from the spirit of the
inventions. The accompanying claims and their equivalents are intended to
cover such forms or modifications as would fall within the scope and
spirit of the inventions.

Patent applications by Akihiko Takeo, Kunitachi-Shi JP

Patent applications by Katsuhiko Koui, Yokohama-Shi JP

Patent applications by Kenichiro Yamada, Tokyo JP

Patent applications by Satoshi Shirotori, Yokohama-Shi JP

Patent applications by KABUSHIKI KAISHA TOSHIBA

Patent applications in class GENERAL RECORDING OR REPRODUCING

Patent applications in all subclasses GENERAL RECORDING OR REPRODUCING